Microwave monolithic integrated circuits (MMIC) used in radio frequency (RF) modules have traditionally been built in low to medium volume. The key elements that prevented this technology from attaining high volume production, similar to surface mount technology components, is the difficulty in working with fragile MMIC chips and the tight tolerances required when manufacturing such components.
A millimeter wave (MMW) module is typically made up of dozens of MMIC chips, substrates and discrete components mounted with epoxy or solder to a Coefficient of Thermal Expansion (CTE) matched carrier or similar machined housing. The radio frequency components are typically connected to other components and terminal pads via wire or ribbon bonds. Tuning of the radio frequency modules after assembly is almost always required.
Although many chip manufacturers are now offering individual MMIC chips in a surface mount package, an entire receiver, transmitter or local oscillator (LO) multiplier have not been provided in a single chip package to enable production of a MMW module with fewer surface mounted components. In addition, the unavailability of a wide array of surface mount MMIC chips has caused designers to shy away from their use because of the requirement to mix bare die with surface mount chips.
Another reason why single transmitter, receiver or LO multiplier MMIC chip packages have not been available is because these types of devices require some level of filtering of unwanted signals. A receiver requires image rejection, a transmitter requires local oscillator (LO) signal rejection, and a frequency multiplier requires filtering of a fundamental frequency. Prior art filters used in conjunction with such devices were traditionally made from thin film material, and were too large to mount into a small chip package. Some prior art devices, however, have been fabricated as a MMW receiver chip using image reject mixers, such as shown in FIG. 1.
FIG. 1 illustrates a receiver chip 20, having a low noise amplifier 22 that receives the radio frequency signal, a capacitor 24 connected to ground, and DC signal coming in and operative at drain voltage Vd. An image reject mixer 26 receives the local oscillator (LO) signal and is operative with in-phase (I) and quadrature (Q) channels. An external L-band hybrid combiner 28 receives the intermediate frequency, as illustrated. These receiver chips have not seen wide commercial acceptance because of their limited image reject performances and the requirement to use an external I/Q hybrid combiner 28 to obtain a single IF output. A hybrid combiner at L-band also is very large in comparison to the high frequency chips used in such devices.